Heretofore, styrenic polymers produced by the radical polymerization or the like have had an atactic configuration in stereostructure, have been molded to a variety of shapes by various molding methods such as injection molding, extrusion molding, blow molding, vacuum molding and cast molding and have been used for electrical appliances, office machines, household goods, packaging containers, toys, furnitures, synthetic papers and other industrial materials.
Because of their atactic configuration in stereochemical structure, however, such styrenic polymers have suffered the disadvantage of inferior heat and chemical resistances.
The group of the present inventors has previously succeeded in developing styrenic polymers each having a high degree of syndiotacticity and further, has proved that crystalline styrenic polymers having syndiotactic configuration are obtained by the use of a catalyst comprising a titanium compound and a contact product (alkylaluminoxane) of an organoaluminum compound with a condensing agent (refer to Japanese Patent Application Laid-Open No. 187708/1987).
The above-mentioned crystalline styrenic polymers are produced by means of slurry polymerization, bulk polymerization or the like and preferably in a high concentration of styrene from the viewpoint of the catalyst activity and polymer productivity. However, the use of a catalyst containing a metal (Al, Ti, Fe, etc.) in the production of the styrenic polymers has caused the problems, depending on the catalytic activity, that the metallic components remain in the polymers thus obtained, the molecular weight thereof is lowered or the color tone thereof is worsened. Therefore, it has been desired to minimize the residual catalyst components in the obtained polymer by means of deashing (removal of residual catalyst).
As a process for the deashing treatment, mention is made of a process in which a deashing agent is added to the polymer to treat the same, a process in which a swelling agent is employed to make the polymer swell, a process in which the treatment temperature is raised in any of the aforementioned processes in order to improve the deashing efficiency and the like processes.
However, these processes involve the problems that the deashing efficiency is low, cleaning is required, a stable operation is difficult and so forth.
Specifically, the process in which a deashing agent is added involves such problems as to necessitate a step of removing the deashing agent and the use of a large amount of a solvent, thereby complicating the process itself and increasing the installation cost.
On the other hand, the process in which a swelling agent is employed is capable of deactivation and deashing under a relatively mild treatment condition, but still involves such problems that the produced polymer is dissolved or agglomerated depending on the composition and conversion efficiency of the resultant polymer, liquid composition of the treating liquid and the treatment temperature, thus making stable operation difficult and moreover, the swelling of the polymer brings about a large amount of a waste liquid containing residual catalyst, thus making it impossible to decrease the quantity of the residual metallic component to a prescribled level or lower.